Internal-combustion engine with an electronically controlled hydraulic system for actuation of the valves and means for compensating changes in the operating conditions of the hydraulic

Abstract

In an internal-combustion engine equipped with an electronically controlled hydraulic system for variable actuation of the inlet and/or exhaust valves of the engine, the hydraulic system for actuation of the valves includes, for each engine valve, a solenoid valve for controlling the corresponding hydraulic actuator. Each solenoid valve is controlled according to a pre-set control criterion according to the operating parameters of the engine, said pre-set control criterion corresponding to reference operating conditions of the hydraulic fluid and, in particular, to the value of viscosity of the hydraulic fluid, which varies with temperature. The aforesaid control criterion is, however, adjusted according to an estimated deviation between reference operating conditions of the hydraulic fluid and actual operating conditions of the hydraulic fluid.

What is claimed is:  
     
       1. An internal combustion engine, comprising: 
       at least one inlet valve and at least one exhaust valve for each cylinder of the engine, each provided with respective elastic return means, which push the valve towards a closed position, for controlling respective inlet and exhaust ducts;  
       at least one camshaft for actuating each inlet and exhaust valve of the cylinders of the engine by means of respective tappets, each inlet and exhaust valve being controlled by a respective cam of said camshaft,  
       in which each of said tappets controls the respective inlet and exhaust valve against the action of said elastic return means by means of the interposition of hydraulic means, which include a pressurized fluid chamber,  
       the pressurized fluid chamber associated to each inlet or exhaust valve being designed for being connected, by means of a solenoid valve, to an exhaust duct for the purpose of uncoupling the valve from the respective tappet and causing rapid closing of the valve as a result of the respective elastic-return means; and  
       electronic control means for controlling each solenoid valve for varying the time and the stroke of opening of the respective inlet or exhaust valve according to one or more operating parameters of the engine,  
       wherein it further comprises at least one temperature sensor in the proximity of the aforesaid hydraulic means for actuating the valves, said electronic control means being programmed for estimating the viscosity of the hydraulic fluid according to the signal at output from said temperature sensor and for controlling each solenoid valve according to the estimate value of viscosity, and  
       wherein the aforesaid electronic control means are programmed for controlling the inlet and/or exhaust valves of the engine according to a pre-set reference criterion based upon operating parameters of the engine, said pre-set reference criterion corresponding to pre-set reference operating conditions and said electronic control means being moreover programmed for correcting said control criterion according to the difference between the reference operating condition and the estimated actual operating conditions, the latter including both the estimated value of fluid viscosity and the value of fluid pressure measured with a pressure sensor.  
     
     
       2. A method for controlling the inlet and/or exhaust valves of an internal-combustion engine, said engine comprising: 
       at least one inlet valve and at least one exhaust valve for each cylinder of the engine, each provided with respective elastic return means, which push the valve towards a closed position, for controlling respective inlet and exhaust ducts;  
       at least one camshaft for actuating each inlet and exhaust valve of the cylinders of the engine by means of respective tappets, each inlet and exhaust valve being controlled by a respective cam of said camshaft,  
       in which each of said tappets controls the respective inlet valve or exhaust valve against the action of said elastic return means by means of the interposition of hydraulic means, which include a pressurized fluid chamber,  
       the pressurized fluid chamber associated to each inlet or exhaust valve being designed for being connected, by means of a solenoid valve, to an exhaust duct for the purpose of uncoupling the valve from the respective tappet and causing rapid closing of the valve as a result fo the respective elastic return means, and  
       in which each solenoid valve is controlled for varying the time and the stroke of opening of the respective inlet or exhaust valve according to one or more operating parameters of the engine,  
       wherein the value of temperature of the hydraulic fluid is detected in the proximity of the aforesaid hydraulic means for actuation of the inlet and/or exhaust valve of the engine, and the value of viscosity of the hydraulic fluid is estimated according to the detected temperature value,  
       and in that the aforesaid solenoid valve is controlled according to the estimated viscosity value, and  
       wherein each solenoid valve is controlled according to a pre-set reference criterion according to operating parameters of the engine, said pre-set reference criterion corresponding to pre-set reference operating conditions, and in that the aforesaid criterion is corrected according to the estimated deviation between reference operating condition and actual operating conditions.  
     
     
       3. The method according to  claim 2 , wherein said actual operating conditions are represented by the estimated value of viscosity of the hydraulic fluid. 
     
     
       4. The method according to  claim 3 , wherein said actual operating conditions also include the measured value of pressure of the hydraulic fluid.